but u.s. commanders want assurances that until then, afghans will guard their back. >> it's their leadership that has to come to play to reduce the threat to us. >> reporter: over the last eight days i've seen a lot of interaction between u.s. and afghan troops. some of it relaxed. but, brian, at all times there's one or two fully battle-dressed american soldiers with their fingers near the trigger, just in case. >> lester holt starting off our coverage in kabul tonight. lest lester, thanks. now to our chief foreign correspondent, richard engel, also in kabul, on what's been accomplished and what hasn't in over a decade now in that country. richard, good evening. >> good evening, brian. this is a country where a group of lightly armed insurgents defeated the soviet union. it seems we haven't won here, either. we haven't lost exactly. mostly, we're leaving this country because we're tired, and tired of writing blank war checks, when the taliban haven't been defeated. this woman is about to die,